Enhanced midinfrared photodetection via composite pyramid silicon structures exploiting localized surface plasmons

We report the fabrication and mid-infrared (MIR) photoresponse characterization of three Ag/n-Si Schottky device structures: planar, inverted pyramid (IPS), and composite pyramid. N-type Si wafers were patterned and etched to produce periodic micro-pyramids, followed by sequential deposition of Ag layers to form the active and electrode regions. Under zero-bias illumination from a 300 °C blackbody source, the planar device exhibits limited responsivity, with 65.21 nA/W at 3.46 μm and negligible response beyond 6 μm. The IPS structure extends the detection range and enhances local electric fields via LSPR, achieving 310.82 nA/W at 3.46 μm. Incorporating a central upright pyramid, the composite structure further amplifies field confinement and hot carrier generation, yielding a peak responsivity of 17.37 μA/W at 3.46 μm and maintaining 0.46 μA/W at 10 μm, representing significant enhancement over IPS. Simulation and experimental results also reveal that the composite design greatly concentrates local fields, improves photon absorption, and enhances hot carrier transport, demonstrating a highly efficient approach for MIR photodetection using Si-based devices.